This invention deals with a siloxane composition used primarily as a transparent coating on solid substrates. More specifically the composition can be used to coat solid substrates to render such substrates abrasion resistant, weather resistant, ultraviolet light, (UV), resistant, and to allow such substrates to be tinted and/or dyed. The compositions of this invention when cured on solid substrates especially polycarbonate, yield uniform, gel free, glossy surfaces to the coated substrates. Current markets for such coatings are well established and will expand as the abrasion resistance and weatherability of these coatings is improved.
The present invention offers significant advantages over many of the known silicone coating compositions in that an amino-organofunctional silane is used instead of the more costly acryloxyfunctional silanes to solubilize and stabilize the colloidal silica. Silicone coating compositions found in the relevant background information such as U.S. Pat. No. 4,455,205 issued Jun. 19, 1984 and assigned to General Electric Company, Schenectady, N.Y., discloses an ultraviolet light curable composition prepared from the addition of a multifunctional acrylate monomer to a mixture of an acryloxyfunctional silane and aqueous colloidal silica. The solvent remaining after mixing the components is removed with heating; a photoinitiator is then added and the composition is UV radiation cured. Similarly, U.S. Pat. No. 4,486,504 issued Dec. 4, 1984 and assigned to General Electric Company, Waterford, N.Y., discloses an ultraviolet light curable composition prepared from the addition of a multifunctional acrylate monomer to a mixture of acryloxyfunctional silanes, and/or glycidoxy functional silanes and aqueous colloidal silica. The solvent remaining after mixing the components is removed with heating; a photoinitiator is then added and the composition is UV radiation cured. Thus, neither of these patents teach the composition or the process of the present invention.
Amino-organofunctional silanes and siloxanes have been incorporated into coating compositions that are used as adhesion promoters and releasing films but never before has colloidal silica been added to these formulations to provide a silicon coating composition which, when cured on a solid substrate provides a transparent abrasion resistant coating firmly adhered thereon. U.S. Pat. No. 4,603,086 and assigned to Dai Nippon Insatsu Kabushiki Kaisha; Shin-Etsa Kagaku Kogyo Kabushiki Kaisha, both of Japan, discloses silicone compounds made by reacting a primary amino-organofunctional silane with a di-or multifunctional acrylic compound by a Michael addition reaction. Similarly, U.S. Pat. No. 4,697,026 and assigned to Dow Corning Corporation, Midland, Mich., discloses silicone compounds made by reacting a primary or secondary amino-organofunctional silane with a di- or multifunctional acryl compound by a Michael addition reaction. The uniqueness of the present invention is found in that it further reacts the products formed from the reaction between an amino-organofunctional silane and multifunctional acrylate with dispersions of colloidal silica to yield a transparent abrasion resistant coating with superior properties.